At NASA’s Dynamics of Flight, there are some helpful diagrams explaining how sound waves move around an airplane as it reaches the speed of sound. “Sound is made up of molecules of air that move. They push together and gather together to form sound waves. Sound waves travel at the speed of about 750 mph at sea level. When a plane travels the speed of sound the air waves gather together and compress the air in front of the plane to keep it from moving forward. This compression causes a shockwave to form in front of the plane… A plane traveling at the speed of sound is traveling at Mach 1 or about 760 MPH. Mach 2 is twice the speed of sound. ”